A variety of electrical-to-mechanical transducers exist. Familiar examples include the electrostatic transducers incorporated in loudspeakers, the electromagnetic transducers incorporated in electric gauges and the piezoelectric or magnetostrictive transducers used, for example, in certain narrow band underwater signalling applications. Conventional electrostatic transducers typically utilize the electrostatic force generated by applying an electrical potential difference between a pair of opposed metal plates separated by an air gap. In an electromagnetic transducer, an electric current causes a force to be applied to a wire maintained in a magnetic field, thereby moving the wire and whatever it may contact. Piezoelectric transducers incorporate certain crystals which change their shape, and thus move slightly, in response to an applied electric field. Magnetostrictive transducers incorporate certain metals which change their shape, and thus move slightly, in response to an applied magnetic field.
For comparison purposes, it is useful to consider transducers having a volume of the order of 100 ml. Conventional electrostatic transducers of this sort have relatively low mechanical impedance (ranging from about 1 to about 100 Newton seconds per meter) and are capable of producing only relatively small forces (typically about 0.05 to about 0.5 Newtons). The mechanical impedance range of electromagnetic transducers is about the same as that of conventional electrostatic transducers, although electromagnetic transducers are capable of producing forces of about 0.5 to about 10 Newtons. Piezoelectric and magnetostrictive transducers, on the other hand, have extremely high mechanical impedance (ranging from about 10.sup.6 to about 10.sup.8 Newton seconds per meter) and generate extremely high forces (on the order of about 10.sup.3 to about 10.sup.4 Newtons). It can thus be seen that there is a conspicuous lack of electrical-to-mechanical transducers which, in the 100 ml. size range, would have a mechanical impedance on the order of about 10.sup.3 to about 10.sup.5 Newton seconds per meter and be capable of producing forces in the range of about 10 to about 10.sup.3 Newtons. The present invention provides an electrostatic transducer which fills this gap in the prior art.